The present invention relates generally to optics, and more particularly, to a bidirectional submarine repeater using unidirectional amplification.
To cope with continuous network capacity demand growth, the network service providers must have a clear roadmap on increasing network capacity in next 5-10 years. In the fiber communication systems, to further boost fiber capacity using the same fiber cable deployment requires the deployed fiber to carry more capacity. Packing optical channels more tightly together in the available C-band spectrum is one approach to increase fiber capacity. Expanding the optical band could be another. Employing a single optical band can provide less than 5 THz useable bandwidth. Expanding from one band to two bands, such as C+L bands, the useable bandwidth can be increased to 8 THz or more. In Submarine transmission systems, the major cost comes from fibers and repeaters. For a 6600 km Atlantic link, the cost, including one fiber cable and repeaters, is close to 1.3 million dollars. A low cost solution for large capacity, and long distance transmission systems in submarine applications is desirable.
In order to have a large capacity transmission, packing the channels in the C and L band is one of the solutions. However, to deliver C-band and L-band signals at the same time in co-propagation will reduce the signal performance due to the Raman gain shifting. The energy from the C-band will transfer to the L-band, which will not only degrade the performance in the C-band, but it will also provide more nonlinearity in the L-band. In order to have two directional transmission (eastbound to westbound and westbound to eastbound), the solution so far has been using one link set (including one fiber cable and repeaters) for eastbound traffic and another link for westbound traffic. However, the additional fiber cable and double repeaters required double the cost to 2.6 million dollars.
Accordingly, there is a need for a bi-directional submarine transmission system that overcomes limitations of existing solutions.